Multimedia Broadcast Multicast Services (MBMS) are being implemented in communication systems. In MBMS, data for a service is transmitted in one or more consecutive MBMS sessions of finite duration. MBMS data for such a session can be transmitted using an MBMS mode across a set of cells called a service area. MBMS data can be transmitted in several modes. MBMS data can be transmitted in synchronized fashion in multiple cells in a service area in what is called a single frequency network (SFN) MBMS mode or SFN mode. MBMS data can also be transmitted independently in non-synchronized fashion in multiple cells in a service area in what is called a single cell (SC) MBMS mode or SC mode. For SFN mode, the base stations in the service area transmit identical MBMS user plane data at the same time and at the same frequency in each of the cells of the service area. For SC mode transmission, the base stations schedule and transmit the user plane data independently in some or all of the cells of the service area.
In existing communication systems, the decision whether to transmit MBMS data for a service using SFN mode or SC mode is normally determined by pre-configuration. The operator may configure a mode for a service which typically is defined for an entire period of the MBMS service. In advanced implementations, the decision on whether to transmit the data in SFN mode or SC mode may be made by a network element (NE) in a radio access network (RAN). In such an advanced implementation, when a MBMS session is initiated, the network element located in the RAN may instruct the base stations that are under the NE's control to probe for interested radio terminals. As used herein, the term ‘interested’ denotes those radio terminals that should or will receive user plane data for the MBMS session. To probe for interested radio terminals, the base stations wake up the radio terminals, perform counting procedures to estimate the number of interested terminals, and then report the results of the counting to the network element, which in turn decides the MBMS mode. Counting procedures are described in the “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Introduction of the Multimedia Broadcast Multicast Service (MBMS) in the Radio Access Network (RAN)” [3GPP TS 25.345] which is included here by reference. This advanced implementation may lead to increased system efficiency, but has a much longer setup time. Moreover, the decision may not be always optimal when the network element decides to use a particular MBMS mode based on fixed parameters. In addition, when multiple NEs in the RAN are involved in the decision, additional communication is needed between those NEs, which lead to increased system complexity.
In some applications, a fast setup of the session may be more important than efficiency. Examples are a Tsunami warning or an emergency video transmission to a public safety group. In such cases, the network elements located within the radio access network may not have enough information about the importance or nature of the data to be transmitted and may decide to use a MBMS mode which may not be optimal for the service.
In other applications, terminals wishing to receive the MBMS service may be highly mobile and may require a specific MBMS mode that supports such high mobility. An example of such an application is the transmission of data to ambulances and fire trucks, where ambulances and fire trucks will be making many cell changes and will benefit from the uniform coverage provided by SFN mode. However, the automatic selection method used by the network element located in the RAN may incorrectly decide to use SC mode based on the sparse distribution of terminals in the service area. Yet other applications may require low latency, for example transmission of real time voice to a public safety group. In such cases, the service provider may prefer to use the smaller buffer size of a MBMS mode. However existing communication systems does not facilitate a service provider to control the MBMS mode of a MBMS session other than through pre-configuration.
Accordingly, there is a need for a solution that would facilitate service providers to control the mode of data transmission in communication systems supporting multimedia broadcast multicast service.
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